Processes for applying layers of semiconductive materials to substrates are already known from the prior art.
According to WO 2009/010142 A2, printed electronic components can be obtained by using a printable ink which comprises an organometallic zinc complex as a precursor compound for the semiconductive zinc oxide. In the organometallic zinc complex used, at least one oximate ligand is present. In addition, this zinc complex is free of alkali metals and alkaline earth metals. In the process according to WO 2009/010142, preference is given to using an organometallic zinc complex which has a ligand selected from 2-(methoxyimino)alkanoate, 2-(ethoxyimino)alkanoate or 2-(hydroxyimino)alkanoate.
J. J. Schneider et al., Adv. Mater. 20, 2008, 3383-3387, disclose printed and flexible field-effect transistors with nanoscale zinc oxide as the active semiconductive material. These nanoscale zinc oxide layers are applied with the aid of a precursor solution, the precursor compound used being organic zinc complexes with (2-methoxyimino)pyruvate ligands.
EP 1 993 122 A2 discloses a process for producing a semiconductive zinc oxide layer as a thin-layer transistor using a precursor solution which can be processed at low temperatures. The precursor solution comprises a zinc salt and a complexing reagent. Suitable zinc salts are zinc nitrate, zinc chloride, zinc sulfate or zinc acetate. The complexing reagents used are carboxylic acids or organic amines.
S. Meiers et al., J. Am. Chem. Soc., 130(51), 2008, 17603-17609, disclose aqueous inorganic inks for the production of zinc oxide TFTs at low temperature. The precursor compound used for the semiconductive zinc oxide is Zn(OH)2(NH3)x. In a two-stage process, this inorganic zinc complex is obtained by reacting high-purity zinc nitrate (99.998%) with sodium hydroxide solution in aqueous solution, followed by the reaction of the zinc hydroxide thus obtained with ammonia. In order to remove the salts formed in the reaction of zinc nitrate with sodium hydroxide solution, numerous removal and washing steps are needed.
The processes described in the prior art for producing semiconductive zinc oxide layers to substrates firstly have the disadvantage that the zinc oxide precursor compounds used are prepared in complex synthesis and purification processes. In addition, some expensive high-purity reactants are used. Furthermore, a disadvantage of the precursor compounds used from the prior art is that the thermal decomposition to obtain zinc oxide affords by-products which remain on the substrate and have to be removed in a further step, or impair the purity and hence the functionality of the zinc oxide layer formed.